Known examples of methods of quantification of ammonia include chemical measurement methods and enzymatic measurement methods. A chemical measurement method that is mainly used is the indophenol method. Examples of the enzymatic measurement methods include methods using glutamate dehydrogenase, as well as methods using glutamine synthetase, NAD (nicotinamide adenine dinucleotide) synthetase, carbamate kinase, carbamoyl phosphate synthetase, or the like.
Examples of the enzymatic measurement methods using glutamine synthetase that have been proposed include a method in which glutamine synthetase is allowed to act on ammonia, adenosine triphosphate (ATP), and L-glutamic acid, and kinase is allowed to act on the produced adenosine diphosphate (ADP) and a kinase substrate phosphorus compound, followed by quantifying the produced kinase reaction product to quantify ammonia (see, for example, Patent Document 1). More specifically, a method in which pyruvate kinase is allowed to act on the produced ADP and phosphoenolpyruvate to produce pyruvic acid, and pyruvate oxidase is allowed to act on the produced pyruvic acid, followed by quantifying the produced hydrogen peroxide by a peroxidase-based color reaction to quantify ammonia has been proposed.
Other examples of the enzymatic measurement methods using glutamine synthetase that have been proposed include a method of quantifying ammonia in which glutamine synthetase is allowed to act on a test liquid containing ammonia in the presence of ATP and L-glutamic acid which are not the components to be quantified, and purine nucleotide phosphorylase is allowed to act on the produced inorganic phosphate in the presence of purine nucleotides, followed by quantifying a produced purine compound with xanthine oxidase (see, for example, Patent Document 2).
Examples of the enzymatic measurement methods using NAD synthetase that have been proposed include a method in which NAD synthetase is allowed to act on a test liquid in the presence of ATP, deamido-NAD, ammonia as an amide donor, and Mg2+, to perform the major reacn, and the NAD produced by the major reaction is subjected to a coenzyme cycling reaction, followed by quantifying a component consumed or produced by the cycling reaction to measure ammonia (see, for example, Patent Document 3).